linux-kernel - [PATCH 2/2] LoongArch: KVM: Skip PMU checking on vCPU context switch

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Message-Id: <20251024072001.3164600-3-maobibo@loongson.cn>
Date: Fri, 24 Oct 2025 15:20:01 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
	Xianglai Li <lixianglai@...ngson.cn>,
	Song Gao <gaosong@...ngson.cn>
Cc: kvm@...r.kernel.org,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] LoongArch: KVM: Skip PMU checking on vCPU context switch

PMU hardware about VM is switched on VM exit to host rather than
vCPU context sched off, PMU is checked and restored on return to
VM. It is not necessary to check PMU on vCPU context sched on
callback, since the request is made on VM exit entry or VM PMU CSR
access abort routine already.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 arch/loongarch/kvm/vcpu.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
index bf56ad29ac15..dc35bf526fe9 100644
--- a/arch/loongarch/kvm/vcpu.c
+++ b/arch/loongarch/kvm/vcpu.c
@@ -148,12 +148,6 @@ static void kvm_lose_pmu(struct kvm_vcpu *vcpu)
 	kvm_restore_host_pmu(vcpu);
 }
 
-static void kvm_restore_pmu(struct kvm_vcpu *vcpu)
-{
-	if ((vcpu->arch.aux_inuse & KVM_LARCH_PMU))
-		kvm_make_request(KVM_REQ_PMU, vcpu);
-}
-
 static void kvm_check_pmu(struct kvm_vcpu *vcpu)
 {
 	if (kvm_check_request(KVM_REQ_PMU, vcpu)) {
@@ -304,7 +298,10 @@ static int kvm_pre_enter_guest(struct kvm_vcpu *vcpu)
 		vcpu->arch.aux_inuse &= ~KVM_LARCH_SWCSR_LATEST;
 
 		if (kvm_request_pending(vcpu) || xfer_to_guest_mode_work_pending()) {
-			kvm_lose_pmu(vcpu);
+			if (vcpu->arch.aux_inuse & KVM_LARCH_PMU) {
+				kvm_lose_pmu(vcpu);
+				kvm_make_request(KVM_REQ_PMU, vcpu);
+			}
 			/* make sure the vcpu mode has been written */
 			smp_store_mb(vcpu->mode, OUTSIDE_GUEST_MODE);
 			local_irq_enable();
@@ -1609,9 +1606,6 @@ static int _kvm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	kvm_restore_timer(vcpu);
 	kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
 
-	/* Restore hardware PMU CSRs */
-	kvm_restore_pmu(vcpu);
-
 	/* Don't bother restoring registers multiple times unless necessary */
 	if (vcpu->arch.aux_inuse & KVM_LARCH_HWCSR_USABLE)
 		return 0;
-- 
2.39.3